'unantennated' originates from 'English', specifically built from the prefix 'un-' (from Old English 'un-' meaning 'not'), the word 'antenna' (from Latin 'antenna'), and the adjectival suffix '-ed'.

'antenna' entered English from Latin 'antenna' (originally meaning 'yard-arm' or 'sail-yard'), later adopted in biological/Neo-Latin usage to mean an insect feeler; 'antennate' (having antennae) formed in scientific usage, and 'unantennated' arose by adding the negative prefix 'un-' to that adjective.

Initially 'antenna' meant 'yard-arm' in Latin; over time it developed the biological sense 'feelers' (in insects), so 'unantennated' came to mean 'not having antennae' and has retained that technical meaning.